Methods For Servicing Subterranean Wells

ABSTRACT

Methods for curing lost circulation in a subterranean well comprise the use of a first and a second lost circulation material. The first lost circulation material is added during the initial preparation of a process fluid. The second process fluid is added to the process fluid at a later time as the process fluid is being pumped into the subterranean well. The first lost circulation may comprise granular or lamellar particles or both. The second lost circulation material may comprise fibers, ribbons or both.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

This disclosure relates to methods for controlling lost circulation in subterranean wells, in particular, fluid compositions and methods for operations during which the fluid compositions are pumped into a wellbore, enter voids in the subterranean-well formation through which wellbore fluids escape, and form a seal that limits further egress of wellbore fluid from the wellbore.

During construction of a subterranean well, drilling and cementing operations are performed that involve circulating fluids in and out of the well. The fluids exert hydrostatic and pumping pressure against the subterranean rock formations, and may induce a condition known as lost circulation. Lost circulation is the total or partial loss of drilling fluids or cement slurries into highly permeable zones, cavernous formations and fractures or voids. Such openings may be naturally occurring or induced by pressure exerted during pumping operations. Lost circulation should not be confused with fluid loss, which is a filtration process wherein the liquid phase of a drilling fluid or cement slurry escapes into the formation, leaving the solid components behind.

Lost circulation can be an expensive and time-consuming problem. During drilling, this loss may vary from a gradual lowering of the mud level in the pits to a complete loss of returns. Lost circulation may also pose a safety hazard, leading to well-control problems and environmental incidents. During cementing, lost circulation may severely compromise the quality of the cement job, reducing annular coverage, leaving casing exposed to corrosive downhole fluids, and failing to provide adequate zonal isolation. Lost circulation may also be a problem encountered during well-completion and workover operations, potentially causing formation damage, lost reserves and even loss of the well.

Lost-circulation solutions may be classified into three principal categories: bridging agents, surface-mixed systems and downhole-mixed systems. Bridging agents, also known as lost-circulation materials (LCMs), are solids of various sizes and shapes (e.g., granular, lamellar, fibrous and mixtures thereof). They are generally chosen according to the size of the voids or cracks in the subterranean formation (if known) and, as fluid escapes into the formation, congregate and form a barrier that minimizes or stops further fluid flow. Surface-mixed systems are generally fluids composed of a hydraulic cement slurry or a polymer solution that enters voids in the subterranean formation, sets or thickens, and forms a seal that minimizes or stops further fluid flow. Downhole-mixed systems generally consist of two or more fluids that, upon making contact in the wellbore or the lost-circulation zone, form a viscous plug or a precipitate that seals the zone.

A thorough overview of LCMs, surface-mixed systems and downhole-mixed systems, including guidelines for choosing the appropriate solution for a given situation, is presented in the following reference: Daccord G, Craster B, Ladva H, Jones TGJ and Manescu G: “Cement-Formation Interactions,” in Nelson EB and Guillot D (eds.): Well Cementing—2^(nd) Edition, Houston: Schlumberger (2006): 202-219, the entire contents of which are hereby incorporated by reference into the current application.

SUMMARY

The present disclosure provides means to seal voids and cracks in subterranean-formation rock, thereby minimizing or stopping fluid flow between the formation rock and the wellbore of a subterranean well.

In an aspect, embodiments relate to methods for treating lost circulation in a subterranean well. A process fluid is prepared that contains a first lost circulation material having a concentration. The process fluid is placed into one or more subterranean lost circulation zones. During process fluid placement, a second lost circulation material having a concentration is added on the fly.

In a further aspect, embodiments relate to methods for cementing a subterranean well. A cement slurry is prepared that contains a first lost circulation material having a concentration. The cement slurry is placed into one or more subterranean lost circulation zones. During cement slurry placement, a second lost circulation material having a concentration is added on the fly.

In yet a further aspect, embodiments relate to methods for completing a subterranean well. A process fluid is prepared that contains a first lost circulation material having a concentration. The process fluid is placed into one or more subterranean lost circulation zones. During process fluid placement, a second lost circulation material having a concentration is added on the fly.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any such actual embodiment, numerous implementation—specific decisions must be made to achieve the developer's specific goals, such as compliance with system related and business related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. In addition, the composition used/disclosed herein can also comprise some components other than those cited. In the summary of the disclosure and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the disclosure and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possessed knowledge of the entire range and all points within the range.

The following definitions are provided in order to aid those skilled in the art to understand the detailed description.

The term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid.

As used herein, the term “process fluid” refers to a pumpable fluid that may be circulated in a subterranean well. Such fluids may include drilling fluids, cement slurries, spacer fluids, pills, chemical washes, completion fluids and gravel-pack fluids. In this disclosure, pumpable fluids have a viscosity lower than 1000 mPa·s at a shear rate of 100 s⁻¹.

In embodiments, the use of lost circulation materials (LCMs) during various well treatments and completion operations helps operators achieve success by preventing the escape of process fluids from the wellbore into a subterranean formation. A blend of different types of LCMs, combining at least two of the following: granular materials, lamellar materials and fibrous materials, can be used. Generally, the granular or lamellar LCM concentration in the process fluid varies between about 1 lbm/bbl and 20 lbm/bbl (2.84 g/L and 56.8 lbm/bbl), or between about 4 lbm/bbl and 12 lbm/bbl (11.4 g/L and 34.1 g/L). Fibrous materials may be added at concentrations between about 0.5 lbm/bbl and about 7 lbm/bbl (1.42 g/L and 14.2 g/L) of process fluid.

One of the challenges associated with the use of LCMs is their tendency to adversely affect mixing and the rheological properties of process fluids. Accordingly, operators have an incentive to add the minimum amount of LCMs to achieve a satisfactory result. In addition, LCMs should be inert with respect to the fluids in which they are added.

Conventionally, LCMs are added during the preparation of a process fluid at a fixed concentration, and are dry-blended with solids (e.g., cement, barite, silica, etc.) before adding water to prepare a slurry. The Applicant has unexpectedly discovered post-addition of a second LCM to a pre-prepared process fluid that already contains a first LCM has beneficial effects. In some embodiments, a synergistic effect is obtained that reduces the total concentration of LCMs necessary to control lost circulation, thereby improving the rheological properties of the process fluid. In addition, the resulting process fluid demonstrates improved efficacy as a vehicle for controlling lost circulation. In some embodiments, Applicant has achieved notable success when granular or lamellar materials (or both) comprise the first LCM, and fibrous materials comprise the second LCM that is added at a later time as the process fluid is pumped into a subterranean well.

In some embodiments, the first LCM may comprise carbonate minerals, rubber, polyethylene, polypropylene, polystyrene, poly(styrene-butadiene), fly ash, silica, mica, alumina, glass, barite, ceramic, metals and metal oxides, starch and modified starch, hematite, ilmenite, ceramic microspheres, glass microspheres, magnesium oxide, graphite, gilsonite, cement, microcement, nut plug and sand. The first LCM may be present in more than one particle size, with d₅₀s centered around about 10 microns, 65 microns, 130 microns, 700 microns or 1000 microns. Mica flakes are particularly suitable components of the particle blend, and the aspect ratio of the flakes may vary between about 30 and about 50.

In some embodiments, the second LCM may comprise high aspect ratio materials including fibers, ribbons or both. Suitable fibers include those made from glass, novoloid polymers, polypropylene, Kevlar™, nylon and polyvinyl alcohol. The fibers may be cylindrical, rectangular, straight or curved. The fiber aspect ratio may vary between about 10 and 1000, or between 10 and 200, or between 10 and 100. Fiber blends of various sizes may also be used. Ribbons may comprise iron, aluminum alloys or both. Glass fibers are particularly suitable, with lengths between about 5 mm and 24 mm, or between about 10 mm and 22 mm. Polymer fibers may have lengths between about 10 mm and 24 mm, or between about 18 mm and 22 mm.

In some embodiments, the first CLM may comprise high aspect ratio materials including fibers, ribbons or both. Suitable fibers include those made from glass, novoloid polymers, polypropylene, Kevlar™, nylon and polyvinyl alcohol and the second CLM may comprise carbonate minerals, rubber, polyethylene, polypropylene, polystyrene, poly(styrene-butadiene), fly ash, silica, mica, alumina, glass, barite, ceramic, metals and metal oxides, starch and modified starch, hematite, ilmenite, ceramic microspheres, glass microspheres, magnesium oxide, graphite, gilsonite, cement, microcement, nut plug and sand. The fibers may be cylindrical, rectangular, straight or curved. The fiber aspect ratio may vary between about 10 and 1000, or between 10 and 200, or between 10 and 100. Fiber blends of various sizes may also be used. Ribbons may comprise iron, aluminum alloys or both. Glass fibers are particularly suitable, with lengths between about 5 mm and 24 mm, or between about 10 mm and 22 mm. Polymer fibers may have lengths between about 10 mm and 24 mm, or between about 18 mm and 22 mm. The second LCM may be present in more than one particle size, with d₅₀s centered around about 10 microns, 65 microns, 130 microns, 700 microns or 1000 microns. Mica flakes are particularly suitable components of the particle blend, and the aspect ratio of the flakes may vary between about 30 and about 50.

In some embodiments, the first CLM and second CLM are the same material.

The manner by which the second LCM is added to the process fluid may be adjusted according to the nature of the lost circulation problem. Applicant has described at least three techniques below. With the benefit of the current disclosure, further techniques can be readily derived by people skilled in the art.

One technique comprises adding the second LCM to a portion of the process fluid. For example, a first portion of process fluid that contains only the first LCM may be initially pumped into the well, followed by a second portion that contains both the first and second LCMs. This technique may allow the lost circulation zone to be fully dialated before the high aspect ratio second LCM is introduced, thereby reducing the total amount of second LCM during the treatment.

Another technique comprises ramping up the concentration of the second LCM during the treatment. For example, the second LCM may be initially added to the process fluid at a concentration of about 1 lbm/bbl (2.84 g/L) and gradually increased to about 10 lbm/bbl (28.4 g/L) during the treatment. Beginning at a lower concentration may allow the LCM to penetrate further into the loss zone and, as the concentration increases, the LCM may then seal off the near-wellbore region.

Yet another technique comprises adding the second LCM to the process fluid intermittently during the treatment. The placement of process fluids is a dynamic procedure, and the lost circulation zone may react to the added stress exerted by the process fluid. It may be beneficial to administer the second LCM several times to achieve optimal effectiveness. A first injection of second LCM may initially seal lost circulation zones but, if the seals becomes destabilized, subsequent injections may repair the seals and strengthen the barrier between the wellbore and the formation.

The second LCM may be added to the process fluid by several means, manually or by various metering devices such as screw feeders. Both approaches are known in industry vernacular as “on-the-fly” addition.

In an aspect, embodiments relate to methods for treating lost circulation in a subterranean well. A process fluid is prepared that contains a first lost circulation material having a concentration. The process fluid is placed into one or more subterranean zones. During the placement of the process fluid, a second lost circulation material having a concentration is added to the process fluid.

In a further aspect, embodiments relate to methods for cementing a subterranean well. A cement slurry is prepared that contains a first lost circulation material having a concentration. The cement slurry is placed into one or more subterranean lost circulation zones. During cement slurry placement, a second lost circulation material having a concentration is added on the fly. Those skilled in the art will recognize that the cement slurry may be employed for either primary or remedial cementing.

In yet a further aspect, embodiments relate to methods for completing a subterranean well. A process fluid is prepared that contains a first lost circulation material having a concentration. The process fluid is placed into one or more subterranean lost circulation zones. During process fluid placement, a second lost circulation material having a concentration is added on the fly.

For all aspects, the concentration of the first lost circulation material in the process fluid may vary between about 1 lbm/bbl and 20 lbm/bbl (2.84 g/L and 56.8 lbm/bbl), or between about 4 lbm/bbl and 12 lbm/bbl (11.4 g/L and 34.1 g/L). Fibrous materials may be added at concentrations between about 0.5 lbm/bbl and about 7 lbm/bbl (1.42 g/L and 14.2 g/L) of process fluid. 

1. A method for treating lost circulation in a subterranean well, comprising: (i) preparing a process fluid comprising a first lost circulation material having a concentration; (ii) placing the process fluid into one ore more subterranean lost circulation zones; (iii) adding a second lost-circulation material having a concentration to the process fluid during placement on the fly.
 2. The method of claim 1, wherein the process fluid is a drilling fluid, a cement slurry, a spacer fluid, a chemical wash, a scavenger slurry, a completion fluid, a pill or a gravel packing fluid.
 3. The method of claim 1, wherein the first lost circulation material is granular, lamellar or both.
 4. The method of claim 3, wherein the first lost circulation material comprises mica.
 5. The method of claim 1, wherein the second lost circulation material has an aspect ratio between 10 and
 1000. 6. The method of claim 5, wherein the second lost circulation material is fibrous.
 7. The method of claim 1, wherein the second lost circulation material is added to a portion of the process fluid, added such that the concentration of the second lost circulation material is ramped up during placement, or added intermittently during placement.
 8. A method for cementing a subterranean well, comprising: (i) preparing a cement slurry comprising a first lost circulation material having a concentration; (ii) placing the cement slurry into one or more subterranean lost circulation zones; (iii) adding a second lost-circulation material having a concentration to the cement slurry during placement on the fly.
 9. The method of claim 8, wherein the first lost circulation material is granular, lamellar or both.
 10. The method of claim 9, wherein the first lost circulation material comprises mica.
 11. The method of claim 8, wherein the second lost circulation material has an aspect ratio between 10 and
 1000. 12. The method of claim 11, wherein the second lost circulation material is fibrous.
 13. The method of claim 8, wherein the second lost circulation material is added to a portion of the cement slurry, added such that the concentration of the second lost circulation material is ramped up during placement, or added intermittently during placement.
 14. A method for completing a subterranean well, comprising: (i) preparing a process fluid comprising a first lost circulation material having a concentration; (ii) placing the process fluid into one or more subterranean lost circulation zones; (iii) adding a second lost-circulation material having a concentration to the process fluid during placement on the fly.
 15. The method of claim 14, wherein the process fluid is a drilling fluid, a cement slurry, a spacer fluid, a chemical wash, a scavenger slurry, a completion fluid, a pill or a gravel packing fluid.
 16. The method of claim 15, wherein the first lost circulation material is granular, lamellar or both.
 17. The method of claim 16, wherein the first lost circulation material comprises mica.
 18. The method of claim 14, wherein the second lost circulation material has an aspect ratio between 10 and
 1000. 19. The method of claim 18, wherein the second lost circulation material is fibrous.
 20. The method of claim 14, wherein the second lost circulation material is added to a portion of the process fluid, added such that the concentration of the second lost circulation material is ramped up during placement, or added intermittently during placement. 